The purpose of this research is to improve the activity of the working group studysubjects with a high school biology curriculum materials to formulate indicators throughcooperative learning model based Lesson Study. The subjects studied are students of S1 ProdiBiology Education V semester who take courses Assessing middle and high school biologycurriculum. Research-based Lesson Study is conducted in stages Plan, namely stages ofpreparingLesson Plan; Do, namely the implementation and observation; and See, that is the analysis andreflection for improvement next meeting. Data were collected through observation, analysis ofdocuments, interviews, and questionnaires. The results showed that increased activity group workaccumulated on student interaction in the learning process. Interactions in group work there wasan increase in each cycle, the first cycle of student interaction in the learning process reaches83.5%, cycle 2, cycle 3 and cycle 4 reaches 100%, meaning that all group members listen peertutoring activities, activity inquire, issuing activity opinions, and always respect the opinionsekelompoknya friends, so that the interaction between students and students, students withlearning resources and students with teachers.